At last, M. Night Shyamalan has decided to let his freak flag fly, and made the sort of unapologetic B-movie one always suspected he had pent up inside of him; it swerves from dark comedy to 1970s-esque psycho-horror as the irresistibly preposterous script struggles for attention against a delirious lead performance by James McAvoy. Split is funnier, campier, and more freewheeling than anything its writer-director has done